Abstract:

The energy saving effect of low-pressure(LP) economizer of a 220 MW unit was tested under multivariate factors. Using equivalent enthalpy method, the energy saving effect of LP economizer at different operation modes and different operating parameters has been calculated. For 200MW grade units, when it is necessary to have higher water flow rate and inlet temperature of LP economizer, the condensate water from NO.6 LP heater outlet should be used priority. Under the condition of 220 MW, the optimal flow rate into LP economizer is about 250 t/h, increasing thermal efficiency of the unit by 0.645%. If the inlet water is from the outlet of NO.7 and NO.8 LP heater, the LP economizer inlet temperature is lower, the outlet of the LP economizer should return to the outlet of NO.6 LP heater. And water temperature at LP economizer outlet should be slightly higher than that of NO.6 LP heater outlet. Otherwise, the energy efficiency will decrease compared with the best condition. Under the condition of 220MW, 370 t/h condensate water is extracted from outlet of NO.8 and NO.7 LP heater, entering main condensate water pipe at outlet of NO.6 LP heater after heated. The heating efficiency of the unit increases 2.003%. For different LP economizer operation mode, there are an optimal water returning location and optimal inlet flow.

Key words: boiler, low pressure economizer, energy saving effect, multi-variable factors, equivalent enthalpy method